Adolescence, the transition between childhood and adulthood, coincides with pubertal development, which is a time of remarkable psychological, physical, hormonal and social changes ? a pivotal and critical transition for adolescents with autism spectrum disorder (ASD). A variety of physiological changes also occur which is evident in primary regulatory systems including the Hypothalamic-Pituitary-Adrenal (HPA) axis and the Parasympathetic Nervous System (PNS). These changes result in patterns of enhanced arousal and response to perceived stressors, which have led to a puberty-HPA stress hypothesis. Although this enhanced responsivity may help prepare the individual to adapt to increased demands and new challenges, it may increase vulnerability in youth with ASD who are already prone to enhanced physiological arousal and poor adaption to change. Collectively, findings from the research team have shown: 1) children with ASD exhibit more variability in physiological regulation and heightened response to stress over development, 2) higher cortisol to social interaction and lower cortisol to social threat in ASD, 3) a significant rise in emotion dysregulation (e.g., anxiety) in adolescence, 4) strong associations between social functioning, stress, and pubertal status, and 5) developmental transitions are pivotal to predicting risk and resiliency in individuals with ASD. Thus, we posit that there is significant need for enhanced study of the interplay between social and emotional functioning and stress across pubertal development to examine this potentially susceptible period in ASD. To examine developmental changes across puberty, the study will utilize a cross-sequential design by assessing male and female) children with ASD or typical development (TD) between 10 and 15 years measured longitudinally by following two cohorts for four years. Cohort 1 enrolled at 10-years (follow 10 to 13) and Cohort 2 enrolled at 12-years (follow 12 to 15) will be measured annually for four years. The cross- sectional or cohort effects will be tested when participants are 12 and 13 years of age. Pubertal development change will be examined by physiological (cortisol, Testosterone, Respiratory Sinus Arrhythmia), behavioral (clinical, behavioral coding) and interpersonal (self-report and parent report) measures taken before and after social tasks. The results from this investigation may provide better understanding of the physiological and psychological processes and changes over pubertal development in children and youth with ASD. Moreover, these indices will be examined in relation to social functioning and emotional well-being to reveal potential relationships with comorbid conditions such as anxiety and depression. Thus, the overarching goal is to examine stress and arousal across pubertal development in ASD to ultimately identify potential risk factors, treatment targets, and therapeutic strategies.